Flexible insulating material



July 22, 1930. l v ADAMS 1,771,367

FLEXIBLE INSULATING MATERIAL Filed NOV. 8, 1926 EGELLED O/L Inventor Patented July 22, 1930 UNITED STATES PATENT OFFICE LESTER V. ADAMS, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK FLEXIBLE IN SULATING MATERIAL Application led November 8, 1926. Serial No. 146,929.

The present invention comprises a new laminated product which is of particular utility for electrical insulating purposes.

For some purposes, electrical insulating material should possessv flexibility which is retained even when subjected to relatively high temperatures during the operation of the devices in which the insulation is em-V ployed. For example, for the insulation of some forms of electrical windings -itis desirable to employ a tape consisting of strips of paper between which are held flakes of mica, the composite parts being held together by a soft, flexible binder. Heretofore, an asphaltic composition has been used as a binderybut it has been found that after the tape has been subjected to thev moderately elevated temperatures at which electrical machinery is operated, say a temperature Aof about to 125o C., the asphaltic binder tape becomes brittle and loses its mechanical strength. Many attempts have been made to find a better binder for lthe purpose than an asphaltic composition, but Without success. No binder could be found which combined with flexibility other desired properties, such as high dielectric strength, imperviousness to moisture and oil, and `which `did not heat up and cause relatively high power loss in an alternating electric field.

I have discovered that an improved flexible insulation, and in particular a flexible laminated product, may be prepared by utilizing a drying oil which has been heated for sufficient length of time at a sufficient temperature to carry the oil through the gel stage to the condition of a thick liquid. This material will be referred to hereinafter by the term degelled oil. I have found that a laminated product, such as mica. tape, having its component parts joined together by degelledoil not only remains flexible for long periods of time, vbut has the combination of electrical and physical properties desired for electrical insulation.

An article embodying my invention is illustrated in the accompanying drawing, Fig. 1 showing in perspective a laminated insulating sheet material, one layer being cut away, and Fig. 2 being an enlarged diagrammatic cross sectional view of a fragment of such insulation.

In carrying out n=y invention a drying oil, such as linseed oil, perilla oil or a china wood oil, or a semi-drying oil such as castor oil, is heated inthe usual Well-,understood manner to produce conversion of the oil to a semisolid4 condition which is sometimes referred to as the gel state. The heating time is continued at' a temperature which variessomewhat with' the particular oil, but in general approximates 200 C., until theV gel is. reconverted to the liquid state.' `Linseed oil when thus degelled has a consistency of a thick molasseswhen cooled to room temperature. Chinawood oil is more easily degelled when mixed with a small amount, say about 1%, o-f'an oil which is readily'degelled, as, for example, linseed oil. The degelled oil also may be used in conjunction'- with natural gums, or condensation products, such as-k copal and cumar, for example. y

I prefer to first impregnate a paper sup=- port for the mica with a degelled oil, preferably degelled linseed oil. This o'il may be applied to the paper in solution. Various solvents may be used, for example, 55 naphtha may be mentioned as a satisfactory solvent. A suitable paper, such as rice paper, may be drawn through the solut-ion A'of one part by weight degelled oil and three parts solvent, thereby impregnating the paper. .The impregnated paper is baked at 140 C.

-for about one to two hours. Paper indicated at 1 in the drawing is coated with a layer of Adegelled oil applied without a solvent, for

example, by painting the oil ori the surface of the paper. For the latter purpose, I prefer to use degelled china wood oil. One or more layers 2 of mica flakes or splittings arc applied upon the coated paper, preferably while the degelled oil is kept in afluid state by passing the material -over a heated surface. In Fig. 2, the mica layers are indicated for the sake of simplicity as a single unbroken layei` 2. Degelled oil is applied on the upper surface of the mica splittings, and A finally a layer of paper 3, which has been impregnated as above described with a solution of degelled linseed oil, is superimposed upon the coating of mica flakes. The component parts 'preferably are pressed together by rollers to thoroughlyr consolidate the different layers. The degelled oil is suliciently adhesive to prevent undue slipping of the component parts of the laminated material thus produced. The rollers either may be heated or a roller may be applied to the material while on the hot plate.

The product thus made preferably is baked at about 140 C. for about onehour to render the oil somewhat rubbery. a state which I may terml as cured degelled oil.

Tests have shown that at about 100 C.

electric power losses in insulation made in accordance'with my invention are about onefourth las great as. or even less than. in a similar product made with an asphalticbinder.

What I claim as new, and desire to secure by Letters Patent of the United States, is:

1. An electrical insulation comprising` laminations of flexible insulating material cemented with a .flegellerL dryingr oilr 2. A laminated product. comprising mica flakes having the component parts thereof joined together by cured, degelled, dryingoil.

fAn insulating material comprising a support of flexible material and one or more layers of mica flakes cemented thereto by a degelled oil.

4. Insulating tape comprising strips of paper impregnated with degelled oil and flakes of mica interposed therebetween and held in place by films or" cured, degelled oil.

In witness whereof, I have hereunto set my hand this 5th day of November, 1926.

LESTER V. ADAMS. 

